This invention relates to a method and apparatus for determining the efficiency of a vacuum in a steam sterilizing apparatus. More particularly, the invention is directed to a test device that meets the Bowie-Dick test procedure.
Steam sterilization is a common method of sterilizing items in health care centers and is enhanced when the items are subjected to a vacuum prior to exposure to steam. Since the presence of air can compromise steam penetration into the items being sterilized, a test had to be devised to indicate if any air was present after being subjected to a vacuum.
Such a test was developed by J. H. Bowie and J. Dick and published in an article appearing in "The Lancet", Mar. 16, 1963, pages 586-587. It utilizes a sheet of paper to which a steam sensitive tape is applied in the fashion of a St. Andrew's cross. The sheet is placed in the center of a stack of towels and the combination is then placed in the front bottom of an empty sterilizer chamber and then subjected to a vacuum steam cycle. If for any reason residual air is present in the pack or the chamber, its presence is detected by this construction. It is believed that when steam is introduced into the chamber, any residual air is pushed to the center of the pack or drawn into the pack by pressure differentials. This is shown by the center of the cross pattern showing no reaction to steam presence. If no air were present, the cross pattern would be uniformly changed in color.
This construction was used (with minor changes) until 1982, when Augert (U.S. Pat. No. 4,486,387) taught that various porous papers can be reliably substituted for towels, and then stacked in such a way as to form a pack equivalent to the original Bowie-Dick test pack. In 1983, Bruso (U.S. Pat. No. 4,579,715) taught that by partially occluding the outer surface of this stack of sheets, only one porosity value for the paper need be used and the size of the paper could be reduced. Both patents rely on the porous nature of the specific papers.
Bruso teaches that non-porous layers can be placed on a pack of porous layers to reduce the surface area of exposed porous material to establish a more challenging test for the evacuation of air and introduction of steam. This also results in a smaller test pack, but Bruso's pack still requires porous pads such as a stack of blotter papers disposed on either side of an indicator sheet.
An ideal Bowie-Dick test device should not be larger than necessary and should be easily manufactured, reliable and consistent. It should not generate any waste material and it should become a permanent test record. An object of the present invention is to provide such an improved Bowie-Dick test device.